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Understanding flea biology key to busting resistance speculation

During the past decade, there has been enormous improvements made in flea protection products for use on pet animals and in the environment.

The emergence of the topical adulticides, such as imidocloprid, fipronil and selemectin, has revolutionized flea control in the United States. In addition, the pre-adulticides that include lufenuron, methoprene and pyriproxyfen also have proven effective in flea control. Unfortunately, there has been speculation recently that the common cat flea (Ctenocephalides felis) has demonstrated resistance to some of these chemicals. This is considered to be a misconception among most flea biologists and veterinary dermatologists, and the true "resistance" stems from the lack of knowledge of flea biology, existing resistance to older adulticides and poor compliance (See suggested reading).

Biology revisitedCtenocephalides felis (C. felis) is the common flea found on most domesticated animals. This cat flea is found on cats, dogs, raccoons, opossums, domesticated rabbits, ferrets, cattle, foxes, coyotes, bobcats, koalas and some avian and rodent species. It is also found to infest the mongoose population in Hawaii. They are rarely found on squirrels or wild rabbits. C. felis stays permanently on these hosts, where they feed, breed and eventually die.

They do not survive for extended periods of time off the host, however, survival rates of 12 days or more were reported under moist conditions in homes. In addition, adult fleas may, on occasion, leap onto clothing of humans and be carried away to a new location.

Fleas are obligate parasites and are a permanent parasite on the host until it dies, usually in about 100 days. The average pet has twice as many female fleas as male fleas. The female flea begins feeding on the pet and starts to lay eggs within 24 hours of hatching and can lay up to 40-50 eggs per day.

The eggs are not sticky and fall off the pet into the environment. It has been clearly shown that many eggs do not survive and undergo desiccation in dry environments. However, due to the massive reproductive capabilities of the adult flea, a substantial infestation can still occur in the home as well as the outdoors.

The ova of C. felis begin hatching within a few days after they enter the environment (home and outdoors). The proper conditions for survival include adequate temperature (probably the most important factor) and humidity. The ideal temperature is 40-85 degrees F and humidity above 50 percent. Dry conditions with humidity below 50 percent can be lethal to ova. Ova and larvae simply desiccate when exposed to hot and dry conditions with inadequate moisture.

The surviving eggs hatch into larvae within a few days or weeks. The larvae also undergo several moltings. Larvae survival is also dependent upon similar temperature and humidity values as the ova but also are reliant on a food source: adult flea feces (dried host blood). The larvae enter the pupal stage by spinning a loosely packed silk cocoon. This sticky cocoon often is coated with environmental particles and is much more resistance to extreme environmental conditions and insecticides. Pupae will hatch in 13 days or less under ideal conditions, but may survive for five months or more without an adequate host. The time for pupal development and hatching is termed the pupal window.

The time from deposition of eggs to adult-flea emergence is called the developmental window and can be up to three months in duration. These pre-adults are found in the carpeting fibers, pet bedding, under furniture, cracks in hardwood floors, under sofa cushions, soil, grass, sand and in animal burrows.

When encountering a flea infestation on a pet, especially a pet with symptoms of flea allergy dermatitis, a three-step program is recommended to eliminate or reduce flea bites on the pet.

Initially, the proper application of adulticides, such as fipronil, imidocloprid or selemectin, on all pets is advised. Some of these products demonstrate larvicidal properties.